Three questions...

Firstly I'm struggling a little with understanding how to size the pump for a single zone system.

Details: 1300sqft shop. 1250' of Pex already installed. Slab is fully insulated with 2" of foam. Radiant as secondary heating/floor conditioning only, not main heat source.

How do I decide on a pump size here? There are large differences on how much water each pump can move. Is a smaller pump going to be appropriate? Looks like it will be connected to a small DHW tank. Electric or propane is all I have access to. Everything else on site is electric.

Second question is about simple thermostat control. I was looking at the in slab thermostats. They seem to be the best thing when conditioning the slab only. If I was heating the whole place with radiant, then air sensor would be fine. Am I looking at this the right way?

Third question is whether or not it is possible to wire the system so that it can be switched onto a generator in case of blackout? I can run a small DHW tank and thermostat with the generator I have at present. I'm not sure about the power demands of the pumps though. I guess what I am wondering is if the system can be wired to be plug connected as opposed to direct wired to the breakers? I may not be installing a full size generator backup system. So at present I only have a smaller unit.

Any thoughts or suggestions would be greatly appreciated. Even if they are to say I am totally out to lunch.

Thanks